Aquatic Plans vs Land Plants and Nutrients
Location: Outside U.S.
Date: Summer 2011
My students have many question about plants growth. Many plant need soil to grow and make food. What kind of soil need in aquatic plants to grow or this normal soil is used for the aquatic plant?
You may recall the famous experiment by Jan Baptist van Helmont where he grew a tree in a large pot with a weighed amount of soil for five years and determined that the bulk dry weight of the tree did not come from the soil but rather from the carbon dioxide drawn from the air (with water contributing to the fresh weight). The experiment demonstrates that the soil is most critical for supplying physical support and trace minerals. In an aquatic environment, the trace minerals are found primarily in the water so the soil largely serves as a means to anchor the aquatic plant and keep it from drifting.
Aquatic plants, by definition, thrive in what are called hydric soils. Hydric is a general term that can include many distinct soil types. However, these soils share one commonality – they are flooded or ponded long enough to develop anaerobic (meaning they lack oxygenated) conditions.
Hydric soils typically have a dark surface horizon with organically rich topsoil. Immediately underneath, there is a gray/blue horizon. These colors are imparted to the soil due to the anaerobic conditions (indicating that oxygen is deficient). If the soil is drained of water, it can undergo chemical reactions and become orange/red (indicating that oxygen is plentiful). In many cases, the soil may have a marbled appearance with gray/blue and orange/red pockets, indicating uneven drainage. There are also some simple smell cues that can indicate hydric soils: for instance, a hydrogen sulfide odor (rotten egg smell).
Bear in mind that aquatic plants still have the same general metabolic requirements that terrestrial plants have. In particular, they have evolved unique mechanisms to transport oxygen to their flooded root zones. For instance, aerenchyma cells in rice basically act as a snorkel, supplying oxygen for respiration. If a rice plant is totally submerged due to a monsoon, then the snorkel cannot deliver oxygen, and the plant drowns. At the International Rice research Institute in the Philippines, scientists have developed a variety of rice that can survive extended periods of time totally submerged!
Dr. Tim Durham
Instructor, Office of Curriculum and Instruction
Department of Biological Sciences
Florida Gulf Coast University
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Update: June 2012